Effect of the Heat Input and Ageing Treatment on Microstructure and Mechanical Properties of AISI 317L Stainless Steel Dissimilar Welded Joints

The present work investigated the influence of heat input and aging time on the microstructural characteristics and the mechanical properties of dissimilar AISI 317L austenitic stainless steel welded joints. The AWS ER2209 wire-electrode was used as filler metal, and two different heat input levels were applied (4 and 8 kJ/cm), aiming to verify the influence of this parameter on the deleterious phases precipitation. An aging heat treatment (AHT) was carried out at 700 °C for two different exposure times: 50 and 100 hours. It was observed that aging promoted a refinement of the base metal region, and all delta ferrite was transformed into the sigma phase. The microstructure of the fusion zone (without AHT) presented a significant amount of austenite that precipitated in three different morphologies: allotriomorphific of grain boundary, Widmanstätten, and intragranular. For all the thermally treated samples, it was possible to identify the presence of the σ and χ phases. Additionally, the highest concentration of the χ phase was identified in the samples submitted to 50 hours of AHT. The welding condition and AHT that presented joints with higher mechanical resistance and remarkable toughness were those welded with 4 kJ/cm heat input and with 100 hours of AHT. All welded joints showed an increase in the hardness profile after AHT. The microhardness values showed a good correlation with the microstructure and the mechanical tests so that the highest values of microhardness were observed in welded joints with heat input of 4 kJ/cm and 100 hours of AHT

Keywords:
AISI 317L Steel; Electrode AWS ER2209; Aging heat treatment; Microstructure; mechanical properties